At least 40 school children at the Outwood Academy in northern England were struck by a mysterious "illness" with at least two being taken to the hospital, leaving responding crews trying to figure out what happened.

Police and ambulances were called out to the academy in Ripon, roughly 240 miles north of London, after students started collapsing shortly after 11 a.m., according to the Independent.

"A number of students had collapsed at the school and have been taken to [hospital]," a North Yorkshire Police spokesperson said. "At this time, the safety of all the students and staff at the school is paramount and officers are working with the fire and ambulance services to establish what has caused the students to collapse."

The North Yorkshire Fire and Rescue Service said it had received a call around lunchtime about reports of students "falling ill suddenly with nausea and feeling faint," according to CBS News.

"A specialist detection, identification and monitoring (DIM) team from West Yorkshire Fire and Rescue Service is also at the incident," the service said in a statement. 

Forty students were treated on site, and all were able to be released back to their classes, or at the end of the school day, according to the BBC.

Though fire officials are still investigating what caused the students to collapse, some believe the students who fainted had become overwhelmed due to heat, while the rest may have succumbed to "mass hysteria."